1. Technical Field
The disclosure relates to a carrier recovery device and a carrier recovery method, and more particularly to a carrier recovery device and a carrier recovery method under a low carrier wave.
2. Related Art
Carrier waves may be applied in various different fields, for example television signal transmission, transmission of speech signals in communication, etc. When the data to be sent has a low frequency, the transmission is easily interfered if the data is sent at the original data frequency, which is disadvantageous for reception. At this time, the data may be transmitted using a carrier wave. First, a signal of the data is loaded in a signal of the carrier wave; then, a receiving end receives the data signal at a frequency of the carrier wave; finally, the received carrier wave signal is demodulated to obtain the original data signal.
In brief, the carrier wave is a technology for assisting signal propagation, which may adjust a signal to a frequency many times higher than that of the original signal, so that the transmission of the signal is not easily interfered with. Afterwards, once the carrier wave signal is received, the carrier wave is removed so as to restore the original signal.
For example, when receiving conventional television signals from a cable or wireless television station, the television signals have frequencies ranging from 40 MHz to 900 MHz; specifically, the television signals firstly pass through tuners to output intermediate frequency (IF) signals having a frequency of 38 MHz, 38.9 MHz, or 45.75 MHz; then, the IF signals are demodulated according to settings of the turners to generate baseband signals, so as to provide correct pictures and audio signals for being viewed by users.
During this process of demodulation, carrier recovery must be performed on the IF signals at the receiving end, so as to generate a stable demodulated wave that is not easily interfered with. However, conventionally, if the carrier wave intensity of the signal is rather low the carrier recovery tends to be unstable, thereby causing incorrect pictures and sounds.